Methods and Systems Utilizing Ultrasound-Assisted Sampling Interfaces for Mass Spectrometric Analysis

ABSTRACT

An ultrasonic transmitter (95) and detector (e.g., integrated as an ultrasound transducer) utilized in a feedback control system automatically monitors and/or detects surface profile (e.g., shape) of the liquid-air interface and adjusts the flow rate of sampling liquid to ensure that experimental conditions remain consistent at the time of sample introduction during serial samplings. The feedback control can provide for automated adjustment of the surface profile of the liquid-air interface in accordance with changes in desired set point according to an experimental workflow (e.g., automated adjustment between an interface corresponding to a vortex sampling set point and an overflow cleaning set point). Improvements in desorption efficiency and quality of mass spectrometry data by degassing of the liquid solvent utilized within the sampling interfaces, and/or utilization in a feedback control system for generating data indicative of a surface profile of the liquid-air interface within the interface&#39;s sampling port may be realized.

RELATED APPLICATION

This application claims the benefit of priority from U.S. ProvisionalApplication No. 62/589,071, filed on 21 Nov. 2017, the entire contentsof which are incorporated by reference herein.

FIELD

The present teachings generally relate to mass spectrometry, and moreparticularly, to ultrasound-assisted sampling interfaces for massspectrometry systems and methods.

INTRODUCTION

Mass spectrometry (MS) is an analytical technique for determining theelemental composition of test substances with both qualitative andquantitative applications. MS can be useful for identifying unknowncompounds, determining the isotopic composition of elements in amolecule, determining the structure of a particular compound byobserving its fragmentation, and quantifying the amount of a particularcompound in a sample. Given its sensitivity and selectivity, MS isparticularly important in life science applications.

In the analysis of complex sample matrices (e.g., biological,environmental, and food samples), many current MS techniques requireextensive pre-treatment steps to be performed on the sample prior to MSdetection/analysis of the analyte of interest. Such pre-analytical stepscan include sampling (i.e., sample collection) and sample preparation(separation from the matrix, concentration, fractionation and, ifnecessary, derivatization). It has been estimated, for example, thatmore than 80% of the time of overall analytical process can be spent onsample collection and preparation in order to enable the analyte'sdetection via MS or to remove potential sources of interferencecontained within the sample matrix, while nonetheless increasingpotential sources of dilution and/or error at each sample preparationstage.

Ideally, sample preparation and sample introduction techniques for MSshould be fast, reliable, reproducible, inexpensive, and in someaspects, amenable to automation. By way of example, various ionizationmethods have been developed that can desorb/ionize analytes fromcondensed-phase samples with minimal sample handling (e.g., desorptionelectrospray ionization (DESI) and direct analysis in real time (DART),which “wipe-off” analytes from the samples by exposing their surfaces toan ionizing medium such as a gas or an aerosol). However, suchtechniques can also require sophisticated and costly equipment, and maybe amenable only for a limited class of highly-volatile small molecules.Another recent example of an improved sample introduction technique isan “open port” sampling interface in which relatively unprocessedsamples can be introduced into a continuous flowing solvent that isdelivered to an ion source of a MS system, as described for example inan article entitled “An open port sampling interface for liquidintroduction atmospheric pressure ionization mass spectrometry” of VanBerkel et al., published in Rapid Communications in Mass Spectrometry,29(19), pp. 1749-1756 (2015), which is incorporated by reference in itsentirety.

There remains a need for improved sample introduction techniques thatprovide sensitivity, simplicity, selectivity, speed, reproducibility,and high-throughput.

SUMMARY

Methods and systems for improving mass spectrometry (MS) data generatedfrom sampling interfaces having an open sampling port from which aliquid is delivered to an ion source for mass spectrometric analysis areprovided herein. In accordance with various aspects of the presentteachings, MS-based systems and methods are provided in which a sourceof ultrasound energy (e.g., an ultrasonic transmitter) is associatedwith at least one of the sampling interface and a sample substrateconfigured for insertion within the sampling interface so as to provideultrasound energy thereto. In various aspects, the use of a source ofultrasound energy can provide improved desorption efficiency, improvethe quality of the MS data by degassing of the liquid solvent utilizedwithin the sampling interfaces, and/or be utilized in a feedback controlsystem for generating data indicative of a surface profile of theliquid-air interface within the interface's sampling port. In someaspects, for example, an ultrasound energy module coupled to one of thesampling interface or a sampling substrate itself can improve theelution of analytes from a solid-phase sample substrate, for example, byagitating the desorption liquid within the sampling probe so as toincrease the efficiency of mass transfer from the sampling substrate.Additionally or alternatively, the ultrasound energy can be effective toremove bubbles from the liquid delivered to the ion source so as toreduce the presence of aberrations or spikes in the MS data that can beobserved when bubbles are discharged into the ionization chamber.Moreover, in various aspects of the methods and systems provided herein,an ultrasonic transmitter and detector (e.g., an ultrasound transducer)can be utilized in a feedback control system so as to automaticallymonitor and/or detect the surface profile (e.g., shape) of theliquid-air interface (e.g., without human intervention) and adjust theflow rate of the sampling liquid to ensure that experimental conditionsremain consistent at the time of sample introduction for serialsamplings. In such aspects, for example, the ultrasound energy that isreflected from the liquid-air interface can be detected so as to enablethe flow rate of a liquid (e.g., a desorption solvent) into and/or outof a sampling probe to be selectively adjusted so as to maintain adesired liquid-air interface within the sampling port and a stable andreproducible analyte flow of consistent dilution to the ion source,thereby increasing the reproducibility and/or accuracy of the MSanalysis. Additionally or alternatively, the feedback control canutilize the detected ultrasound energy so as to provide for theautomated adjustment of the surface profile of the liquid-air interfacein accordance with a change in the desired set point according to anexperimental workflow (e.g., automated adjustment between an interfacecorresponding to a vortex sampling set point and an overflow cleaningset point between samplings).

In accordance with various exemplary aspects of the present teachings, asystem for analyzing a chemical composition of a specimen is provided,the system comprising a reservoir for storing a liquid and a samplingprobe having an open end partially defining a sample space configured toreceive the liquid from the reservoir, the liquid within the samplespace further configured to receive through the open end one or moreanalytes of a sample. The system can further comprise a pump fordelivering the liquid from the reservoir to an ion source via the samplespace, the ion source being configured to discharge the liquid havingthe one or more analytes entrained therein into an ionization chamber influid communication with a sampling orifice of a mass spectrometer. Anultrasonic transmitter is also provided for applying ultrasound energyto at least one of the liquid within the sample space, the samplingprobe, and a sample substrate to be inserted into the liquid within thesample space. By way of non-limiting example, the sample can be one of aliquid sample containing one or more analytes that can be introduced(e.g., pipetted into the open end of the sampling probe, acousticallyinjected) or a sample substrate having one or more analytes adsorbedthereto such that at least a portion of said one or more analytes aredesorbed therefrom into the desorption solvent within the sample space.

Ultrasonic transmitters can be associated with the sampling probe in avariety of manners. By way of example, in some aspects, in which thesample comprises a sample substrate, the ultrasonic transmitter can becoupled thereto and can be configured to apply ultrasound energy to thesample substrate upon insertion thereof into the sample space (e.g.,under the influence of a controller for activating the ultrasonictransducer upon insertion of the sample substrate within into the samplespace). In such aspects, the ultrasound energy can facilitate desorptioninto the liquid of one or more analytes adsorbed onto a surface of thesample substrate, for example, by agitating (e.g., vibrating) thesubstrate within the liquid and/or by generating heat within thesubstrate and/or liquid so as to increase the elution efficiency of theanalytes. In various aspects, the ultrasonic transmitter can be coupledto the sampling probe so as to apply ultrasound energy to the samplingprobe and the liquid therewithin. In some aspects, for example, theultrasonic transmitter can be disposed in the fluid flow path of theliquid before or after the sample space so as to be in contact with theliquid being flowed through the sampling probe. In various aspects, theultrasound energy can be effective to increase agitation of the liquidwithin the sample space and/or remove bubbles from the liquid deliveredto the ion source so as to reduce the presence of aberrations or spikesin the MS data when bubbles are discharged by the ion source into theionization chamber.

In addition to the above described benefits of the ultrasonictransmitter in accordance with various aspects of the present teachings,in some aspects the ultrasound energy provided by the ultrasonictransmitter can additionally or alternatively be utilized in afeedback-based control system for controlling the surface profile of theliquid-air interface within the open end of the sampling probe. Incertain aspects, for example, the system can further comprise anultrasound detector configured to detect the ultrasound energy that isreflected from the liquid-air interface at the open end of the samplingprobe so as to generate data indicative of a surface profile of theliquid-air interface. A controller, operatively coupled to theultrasound detector, can be configured to generate control signals basedon the surface profile data for adjusting the surface profile of theliquid-air interface, for example, by adjusting the flow rates of theliquid into and out of the sampling probe. By way of non-limitingexample, the control signals generated by the controller are configuredto adjust the flow rate of liquid within the sampling probe by adjustingat least one of the flow rate of liquid provided by the pump and theflow rate of a nebulizer gas that surrounds the discharge end of the ionsource.

Sampling probes in accordance with the present teachings can have avariety of configurations but are generally include an open end by whichthe liquid delivered from the reservoir is open to the atmosphere andthrough which a sample containing or suspected of containing one or moreanalytes can be received. In accordance with various aspects of thepresent teachings, the sampling probe can comprise an outer capillarytube extending from a proximal end to a distal end and an innercapillary tube extending from a proximal end to a distal end anddisposed within said outer capillary tube, wherein the distal end of theinner capillary tube is recessed relative to the distal end of the outercapillary tube so as to define the sample space between the distal endof the inner capillary tube, a portion of an inner wall of the outercapillary tube, and the distal end of the outer capillary tube. In suchaspects, the inner and outer capillary tubes can define a solventconduit and a sampling conduit in fluid communication with one anothervia said sample space, said solvent conduit extending from an inlet endconfigured to receive solvent (e.g., desorption solvent or other liquid)from the reservoir to an outlet end terminating at said sample space.The sampling conduit can extend from an inlet end commencing at thesample space for receiving from the sample space solvent in which theanalytes are entrained to an outlet end fluidly coupled to the ionsource.

In accordance with various exemplary aspects of the present teachings, amethod for analyzing a chemical composition of a specimen is provided,the method comprising providing a flow of liquid to a sampling probe,said sampling probe having an open end partially defining a sample spaceconfigured to receive the liquid and further configured to receivethrough the open end one or more analytes of a sample into the liquidwithin the sample space. The method can further comprise applyingultrasound energy to at least one of the liquid within the sample space,the sampling probe, and a sample substrate at least during insertionthereof into the liquid within the sample space and discharging theliquid having the one or more analytes entrained therein into theionization chamber for ionization therein. In various aspects, theultrasound energy can be generated by an ultrasonic transmitter coupledto at least one of the sampling probe and the sample substrate, themethod further comprising activating the ultrasonic transmitter uponinsertion of a sampling probe into the sample space so as to facilitatedesorption of one or more analytes adsorbed thereto. For example, insome aspects, the ultrasonic transmitter can be coupled to the samplesubstrate and can be configured to apply ultrasound waves to the samplesubstrate upon insertion thereof into the sample space such that theultrasound waves facilitate desorption into the liquid within the samplespace of one or more analytes adsorbed onto a surface of the samplesubstrate. Without being bound by any particular theory, the ultrasoundenergy can be configured to facilitate desorption into the liquid of oneor more analytes adsorbed onto a surface of the sample substrate via atleast one of increasing agitation of the liquid in the sample space andincreasing the temperature of the liquid in the sample space. In variousaspects, the ultrasound energy can be configured to degas the liquidprovided by the pump prior to the liquid being delivered to the ionsource.

In various aspects, applying ultrasound energy can comprise directingthe ultrasound energy through the liquid toward a liquid-air interfaceat the open end of the sampling probe, wherein the method can furthercomprise detecting the reflected ultrasound energy to generate dataindicative of a surface profile of the liquid-air interface at the openend of the sampling probe. Based on the surface profile data, the flowrate of the liquid within the sampling probe can be adjusted so as tocontrol the surface profile of the liquid-air interface.

In accordance with various exemplary aspects of the present teachings, asystem for analyzing a chemical composition of a specimen is provided,the system comprising a reservoir for storing a liquid and a samplingprobe having an open end partially defining a sample space configured toreceive the liquid from the reservoir, the liquid within the samplespace further configured to receive through the open end one or moreanalytes of a sample. The system can further comprise a pump fordelivering the liquid from the reservoir to an ion source via the samplespace, wherein the ion source is configured to discharge the liquidhaving the one or more analytes entrained therein into an ionizationchamber in fluid communication with a sampling orifice of a massspectrometer. The system can additionally include an ultrasonictransmitter for applying ultrasound energy to at least one of the liquidwithin the sample space, the sampling probe, and a sample substrate tobe inserted into the liquid within the sample space and an ultrasounddetector for detecting the ultrasound energy reflected from theliquid-air interface at the open end of the sampling probe so as togenerate data indicative of a surface profile of the liquid-airinterface. Further, the system can include a controller for generatingcontrol signals based on the surface profile data for adjusting thesurface profile of the liquid-air interface. In various aspects, thecontroller can be configured to compare the surface profile data to areference surface profile and to generate control signals for adjustingthe flow rate of liquid within the sampling probe so as to adjust thesurface profile of the liquid-air interface in accordance with thereference surface profile, if necessary. By way of example, the controlsignals generated by the controller can be configured to adjust the flowrate of liquid within the sampling probe by adjusting at least one ofthe flow rate of liquid provided by the pump and the flow rate of anebulizer gas that surrounds the discharge end of the ion source so asto adjust the surface profile of the liquid-air interface.

The liquid within the sample space can receive the analytes thereat in avariety of manners. By way of non-limiting example, the sample cancomprise a liquid sample containing the one or more analytes, which canbe introduced (e.g. by touch, injection, insertion, pipetted,acoustically injected, etc.) into the liquid within the sample space.Alternatively, in some aspects, the sample can comprise a samplesubstrate (e.g., a solid-phase microextraction (SPME) substrate), whichcan have one or more analytes adsorbed thereto. In various aspects, theliquid flowing from the reservoir can comprise a desorption solvent suchthat the analytes are desorbed from the sample substrate when insertedwithin the desorption solvent within the sample space.

The ultrasound detector can have a variety of configurations, but isgenerally configured to generate data indicative of the surface profileof the liquid-air interface at the open end of the sampling probe basedon ultrasound energy received thereat. In some exemplary aspects, theultrasonic transmitter and the ultrasound detector can comprise anintegrated ultrasonic transducer module. In various aspects, theultrasonic transmitter and the ultrasound detector can be disposedrelative to the liquid air interface and one another so as to reflectand detect, respectively, the level of liquid within the sampling spaceat the center thereof.

In response to the detected surface profile, the controller can beconfigured to adjust the surface profile in a variety of manners. By wayof example, the controller can be operatively connected to the pump andcan be configured to adjust the flow rate of liquid within the samplingprobe by adjusting the flow rate of liquid provided to the sample spaceby the pump. Additionally or alternatively, the system can furthercomprise a source of nebulizer gas for providing a nebulizing gas flowthat surrounds the discharge end of the ion source, with the controllerbeing operatively connected to the source of nebulizer gas so as tocontrol the flow rate thereof. In such aspects, the controller can beconfigured to adjust the flow rate of liquid within the sampling probeby controlling a flow rate of nebulizing gas provided to the dischargeend of the ion source.

The sampling probe can have a variety of configurations, but isgenerally configured to receive through the open end the samplecontaining one or more analytes within the liquid (e.g., desorptionsolvent) within the sample space. In various aspects, the sampling probecan comprise an outer capillary tube extending from a proximal end to adistal end, and an inner capillary tube extending from a proximal end toa distal end and disposed within said outer capillary tube, wherein thedistal end of the inner capillary tube is recessed relative to thedistal end of the outer capillary tube so as to define the sample spacebetween the distal end of the inner capillary tube, a portion of aninner wall of the outer capillary tube, and the distal end of the outercapillary tube. In some related aspects, the inner and outer capillarytubes can define a solvent conduit and a sampling conduit in fluidcommunication with one another via the sample space, said solventconduit extending from an inlet end configured to receive the liquid(e.g., desorption solvent) from the reservoir to an outlet endterminating at the sample space. The sampling conduit can extend from aninlet end commencing at said sample space for receiving from the samplespace desorption solvent in which the desorbed analytes are entrained toan outlet end fluidly coupled to the ion source. In certain exemplaryaspects, an axial bore of the inner capillary tube can at leastpartially define the sampling conduit and the space between the innercapillary tube and the outer capillary tube can define the solventconduit. In some related aspects, the controller can be configured toadjust the flow rate of desorption solvent within the sampling probe soas to maintain the surface profile at a reference surface profile byadjusting at least one the flow rate of desorption solvent within thesolvent conduit and the sampling conduit.

Feedback control systems in accordance with various aspects of thepresent teachings can help provide reliable, reproducible results acrossmultiple samplings. By way of example, in certain aspects, thecontroller can be configured to maintain the surface profile at areference surface profile for the serial insertion of a plurality ofsubstrates or serial introduction of a liquid sample. Additionally, insome aspects, the controller can be configured to adjust the surfaceprofile between each insertion of the plurality of substrates. By way ofexample, the controller can be configured to increase the flow rate ofdesorption solvent delivered to the sample space during at least aportion of the duration between each insertion of the plurality ofsubstrates such that desorption solvent overflows from the sample spacethrough the open end of the sampling probe (e.g., so as to clean thesampling probe between the serial insertions). Thereafter, thecontroller can be configured to re-adjust the flow rates such that thesurface profile of the liquid-air interface during the addition of thenext sample is the same as for the previous sample.

In accordance with various exemplary aspects of the present teachings, amethod for analyzing a chemical composition of a specimen is provided,the method comprising providing a flow of liquid to a sampling probe,said sampling probe having an open end partially defining a sample spaceconfigured to receive the liquid and further configured to receivethrough the open end one or more analytes of a sample into the liquidwithin the sample space. The flow of the liquid having the one or moreanalytes entrained therein can be directed from the sample space to anion source configured to discharge the liquid and analytes entrainedtherein into an ionization chamber in fluid communication with asampling orifice of a mass spectrometer. The method can further compriseutilizing an ultrasonic transmitter to generate ultrasound energydirected to the liquid-air interface at the open end of the samplingprobe and utilizing an ultrasound detector to detect the ultrasoundenergy reflected from the liquid-air interface so as to generate dataindicative of a surface profile of the liquid-air interface at the openend of the sampling probe and based on the surface profile data, adjustthe flow rate of the liquid within the sampling probe so as to adjustthe surface profile of the liquid-air interface. In various aspects, themethod can further comprise comparing the surface profile data with areference surface profile, wherein adjusting the surface profile of theliquid-air interface can include adjusting the flow rate of liquidwithin the sampling probe so as to adjust the surface profile at theliquid-air interface in accordance with the reference surface profile.By way of example, the reference surface profile can comprise one of adome-like liquid-air interface and a vortex-like liquid-air interface.

In certain aspects, the liquid provided by the reservoir can comprisedesorption solvent, the method further comprising inserting a firstsubstrate having one or more analytes adsorbed thereto into thedesorption solvent within the sample space exhibiting a referencesurface profile; removing the first substrate from the desorptionsolvent; and adjusting the surface profile of the liquid-air interfaceto the reference surface profile for insertion of a second substratehaving one or more analytes adsorbed thereto into the desorptionsolvent. In some related aspects, the surface profile of the liquid-airinterface can be adjusted between the insertion of the first and secondsubstrates by increasing the flow rate of desorption solvent provided tothe sampling probe such that desorption solvent overflows from thesample space through the open end of the sampling probe during at leasta portion of the duration between insertion of the first and secondsubstrates. Thereafter, the flow rates can then be adjusted (e.g.,automatically without human intervention) for insertion of the secondsubstrate.

In various aspects, adjusting the surface profile of the interface basedon the surface profile data can comprise maintaining substantially thesame volumetric flow rate of liquid provided by the pump while adjustingthe flow rate of nebulizer gas surrounding the discharge end of the ionsource.

These and other features of the applicant's teachings are set forthherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled person in the art will understand that the drawings,described below, are for illustration purposes only. The drawings arenot intended to limit the scope of the applicant's teachings in any way.

FIG. 1, in a schematic diagram, illustrates an exemplary systemcomprising a sampling probe associated with an ultrasonic module andinterfaced with an electrospray ion source of a mass spectrometer systemin accordance with various aspects of the applicant's teachings.

FIG. 2, in a schematic diagram, illustrates an exemplary samplinginterface of FIG. 1 in additional detail, in accordance with variousaspects of the applicant's teachings in which the ultrasonic transmitteris coupled to the sampling probe in accordance with various aspects ofthe applicant's teachings.

FIG. 3, in a schematic diagram, illustrates an exemplary samplinginterface of FIG. 1 in additional detail, in accordance with variousaspects of the applicant's teachings in which the ultrasonic transmitteris coupled to the sample substrate in accordance with various aspects ofthe applicant's teachings.

FIGS. 4A-C respectively depict exemplary MS data generated underconditions in which a) no ultrasonic transmitter is utilized, b) asampling probe having an ultrasonic transmitter coupled thereto as shownin FIG. 2 is utilized, and c) a SPME substrate having an ultrasonictransmitter coupled thereto as shown in FIG. 3 is utilized.

FIG. 5 depicts additional exemplary MS data generated under theconditions of FIGS. 4A-4C.

FIG. 6, in a schematic diagram, illustrates an exemplary samplinginterface in accordance with various aspects of the applicant'steachings in which the ultrasound energy is utilized in afeedback-control system for detecting the surface profile of liquidwithin a sampling probe in accordance with various aspects of theapplicant's teachings.

FIGS. 7A-F schematically depict exemplary surface profile conditionsthat can be detected in accordance with various aspects of the presentteachings.

FIGS. 8A-B depict exemplary MS data generated by the serial insertion ofa plurality of samples within a sampling interface exhibiting a vortexsurface profile (under low-flow conditions) and a dome-like surfaceprofile (under high-flow condition).

FIG. 9 depicts an exemplary schematic block diagram of an implementationof a feedback control system in accordance with various aspects of thepresent teachings.

DETAILED DESCRIPTION

It will be appreciated that for clarity, the following discussion willexplicate various aspects of embodiments of the applicant's teachings,while omitting certain specific details wherever convenient orappropriate to do so. For example, discussion of like or analogousfeatures in alternative embodiments may be somewhat abbreviated.Well-known ideas or concepts may also for brevity not be discussed inany great detail. The skilled person will recognize that someembodiments of the applicant's teachings may not require certain of thespecifically described details in every implementation, which are setforth herein only to provide a thorough understanding of theembodiments. Similarly it will be apparent that the describedembodiments may be susceptible to alteration or variation according tocommon general knowledge without departing from the scope of thedisclosure. The following detailed description of embodiments is not tobe regarded as limiting the scope of the applicant's teachings in anymanner.

In accordance with various aspects of the applicant's teachings,exemplary MS-based analytical systems and methods are provided herein inwhich ultrasound energy can be utilized in association with a samplinginterface having an open sampling port to provide improved desorptionefficiency, improve the quality of the MS data by degassing of theliquid solvent utilized within the sampling interfaces, and/or providefor feedback control based on data indicative of a surface profile ofthe liquid-air interface within the interface's sampling port. In someaspects, for example, an ultrasound energy module can be effective toagitate the desorption liquid within the sampling probe and/or increasea temperature thereof so as to increase the efficiency of mass transferfrom the sampling substrate. Additionally or alternatively, theultrasound energy can be effective to remove bubbles from the liquiddelivered from the sampling probe to the ion source so as to reduce thepresence of aberrations or spikes in the MS data that can be observedwhen bubbles are discharged into the ionization chamber. Moreover, invarious aspects of the methods and systems provided herein, anultrasonic transmitter and detector (e.g., an ultrasound transducer) canbe utilized in a feedback control system so as to automatically monitorand/or detect the surface profile (e.g., shape) of the liquid-airinterface (e.g., without human intervention) and adjust the flow rate ofthe sampling liquid to ensure that experimental conditions remainconsistent between serial samplings (e.g., at the time of each sampleintroduction). In such aspects, for example, ultrasound energy that isreflected from the liquid-air interface can be detected so as to enablethe flow rate of a liquid (e.g., a desorption solvent) into and/or outof a sampling probe to be selectively adjusted so as to maintain adesired liquid-air interface within the sampling port and a stable andreproducible analyte flow of consistent dilution to the ion source,thereby increasing the reproducibility and/or accuracy of the MSanalysis. In various aspects, the feedback control can additionally oralternatively utilize the detected ultrasound energy so as to providefor the automated adjustment of the surface profile of the liquid-airinterface in accordance with a change in the desired set point accordingto an experimental workflow (e.g., automated adjustment between aninterface corresponding to a vortex sampling set point and an overflowcleaning set point between samplings).

FIG. 1 schematically depicts an embodiment of an exemplary system 10 inaccordance with various aspects of the applicant's teachings forionizing and mass analyzing analytes received within an open end of asampling probe 30, the system 10 including an ultrasonic transducer 95configured to apply ultrasound energy to one of the sampling probe 30,the liquid therein, or a substrate for insertion into the open end ofthe sampling probe 30. As shown in FIG. 1, the exemplary system 10generally includes a sampling probe 30 (e.g., an open port probe) influid communication with a nebulizer-assisted ion source 60 fordischarging a liquid containing one or more sample analytes (e.g., viaelectrospray electrode 64) into an ionization chamber 12, and a massanalyzer 70 in fluid communication with the ionization chamber 12 fordownstream processing and/or detection of ions generated by the ionsource 60. A fluid handling system 40 (e.g., including one or more pumps43 and one or more conduits) provides for the flow of liquid from areservoir 50 to the sampling probe 30 and from the sampling probe 30 tothe ion source 60. For example, as shown in FIG. 1, the reservoir 50(e.g., containing a liquid, desorption solvent) can be fluidly coupledto the sampling probe 30 via a supply conduit through which the liquidcan be delivered at a selected volumetric rate by the pump 43 (e.g., areciprocating pump, a positive displacement pump such as a rotary, gear,plunger, piston, peristaltic, diaphragm pump, or other pump such as agravity, impulse, pneumatic, electrokinetic, and centrifugal pump), allby way of non-limiting example. As discussed in detail below, flow ofliquid into and out of the sampling probe 30 occurs within a samplespace accessible at the open end such that one or more analytes can beintroduced into the liquid within the sample space and subsequentlydelivered to the ion source 60. As shown, the system 10 includes anultrasonic transmitter 95 that is configured to generate ultrasoundenergy that can be applied to one of the sampling probe 30 and/or, insome aspects, a substrate 20 that is configured for insertion within theopen end of the sampling probe 30. A controller 80 can be operativelycoupled to the ultrasonic transmitter 95 and can be configured toactivate the ultrasonic transmitter 95 so as to apply ultrasound energyas otherwise discussed herein substantially continuously or for selectedportions of an experimental protocol (e.g., during insertion of thesubstrate 20 within the sampling probe 30), by way of non-limitingexample.

The ultrasonic transmitter 95 can have a variety of configurations butis generally configured to apply or propagate ultrasound energy (e.g.,ultrasonic waves) into one or more of the sample substrate 20, thesampling probe 30, and the liquid contained within the sample space ofthe sampling probe 30, depending on implementation. As will be discussedin detail below with reference to FIGS. 2, 3, and 6, the ultrasoundenergy generated by the ultrasonic transmitter 95 by coupling thetransmitter to the sample substrate 20 or the sampling probe can beeffective to create tiny vibrations within the sample substrate 20, thesampling probe 30, and/or the liquid within the sampling probe 35 thatcan variously facilitate desorption of the analytes adsorbed onto thesurface of the substrate 20 (e.g., via at least one of agitation of thesubstrate 20 and/or liquid, and/or through the generation of heat causedby the vibrations), facilitate degassing of the liquid delivered to theion source 60, and/or facilitate detection of the liquid/air interfaceof the liquid within the open end of the sampling probe. For example, asshown in FIG. 2, at least one ultrasonic transmitter 95 can be coupledin proximity to the open end of the sampling probe 30 (e.g., viaclamping, adhesion, magnetic attraction) such that acoustic wavesgenerated thereby can propagate through the liquid within the samplingspace so as to facilitate desorption through agitation of the liquidabout a sample substrate inserted therein. Without being bound by anyparticular theory, in some additional or alternative aspects, theacoustic energy provided to the liquid within the sample space and/orthe sample substrate 20 can be effective to generate an increase intemperature such that the extraction(binding)/elution(dissociation)equilibrium shifts to the dissociation state (thermodynamically).Likewise, the increased temperature can in some aspects be effective toincrease the mass transfer speed, thereby reducing the time to reachequilibrium (kinetically). In alternative aspects, the ultrasonictransmitter may be mounted on the sample substrate 20 itself or inproximity thereto (e.g., on an actuation mechanism for delivering thesample substrate to the sampling probe 30) as shown in FIG. 3, such thatthe acoustic waves propagate through the sample substrate 20. In variousaspects, the ultrasonic transmitter can comprise a separate ultrasonicprobe, for example, that can be inserted within the liquid of thesampling space 35 (e.g., continuously, intermittently, and/or during theinsertion of a sample substrate 20).

Ultrasonic transmitters 95 suitable for use in accordance with thepresent teachings can be configured to convert electrical energy intoacoustic ultrasonic waves at a wide range of ultrasonic frequencies. Byway of non-limiting example, the ultrasonic energy can exhibit afrequency of at least about 16 kHz, though ultrasonic waves of otherfrequencies can also be utilized in accordance with the presentteachings. By way of non-limiting example, the ultrasound transmitter 95can be a piezoelectric transducer, which includes a piezoelectriccrystal that is configured to change size when a voltage is applied(e.g., ferroelectric piezoceramic crystalline materials such as leadzirconate titanate (PZT)). Alternatively, the ultrasonic transmitter 95can be a capacitive transducer that utilizes electrostatic fieldsbetween a conductive diaphragm and a backing plate to generate theultrasonic wave. Further, a person skilled in the art will appreciatethat other ultrasonic transmitters 95 known in the art and modified inaccordance with the present teachings can be suitable for use with thepresent principles as described for example with reference to system 10.

It will be appreciated that the controller 80 can be implemented in avariety of manners in accordance with the present teachings, butgenerally comprises one or more processors configured to generatecontrol signals for controlling the operations of various elements ofthe system 10 as otherwise discussed herein. For example, the controller80 can be configured to generate control signals such that theultrasonic transmitter 95 generates ultrasound energy substantiallycontinuously or for selected portions of an experimental protocol (e.g.,during insertion of the substrate 20 within the sampling probe 30), byway of non-limiting example.

In accordance with certain aspects of the present teachings, thecontroller can comprise a digital processor executing one or moresequences of instructions contained in memory, which may be read intomemory from another computer-readable medium (e.g., a floppy disk, aflexible disk, hard disk, magnetic tape, or any other magnetic medium, aCD-ROM, digital video disc (DVD), a Blu-ray Disc, any other opticalmedium, a thumb drive, a memory card, a RAM, PROM, and EPROM, aFLASH-EPROM, any other memory chip or cartridge, or any other tangiblemedium from which a computer can read). Execution of the sequences ofinstructions contained in memory causes processor to perform the processdescribed herein. Alternatively hard-wired circuitry may be used inplace of or in combination with software instructions to implement thepresent teachings. Thus implementations of the present teachings are notlimited to any specific combination of hardware circuitry and software.In various embodiments, the controller 80 can be connected to one ormore other computer systems across a network to form a networked system.The network can include a private network or a public network such asthe Internet. In the networked system, one or more computer systems canstore and serve the data to other computer systems. The one or morecomputer systems that store and serve the data can be referred to asservers or the cloud, in a cloud computing scenario. The one or morecomputer systems can include one or more web servers, for example. Theother computer systems that send and receive data to and from theservers or the cloud can be referred to as client or cloud devices, forexample.

The ion source 60 can have a variety of configurations but is generallyconfigured to generate analytes contained within a liquid (e.g., thedesorption solvent) that is received from the sampling probe 30. In theexemplary embodiment depicted in FIG. 1, an electrospray electrode 64,which can comprise a capillary that is fluidly coupled to the samplingprobe 30, terminates in an outlet end that at least partially extendsinto the ionization chamber 12 and discharges the desorption solventtherein. As will be appreciated by a person skilled in the art in lightof the present teachings, the outlet end of the electrospray electrode64 can atomize, aerosolize, nebulize, or otherwise discharge (e.g.,spray with a nozzle) the desorption solvent into the ionization chamber12 to form a sample plume comprising a plurality of micro-dropletsgenerally directed toward (e.g., in the vicinity of) the curtain plateaperture 14 b and vacuum chamber sampling orifice 16 b. As is known inthe art, analytes contained within the micro-droplets can be ionized(i.e., charged) by the ion source 60, for example, as the sample plumeis generated. By way of non-limiting example, the outlet end of theelectrospray electrode 64 can be made of a conductive material andelectrically coupled to a pole of a voltage source (not shown), whilethe other pole of the voltage source can be grounded. Micro-dropletscontained within the sample plume can thus be charged by the voltageapplied to the outlet end such that as the liquid or desorption solventwithin the droplets evaporates during desolvation in the ionizationchamber 12 such bare charged analyte ions are released and drawn towardand through the apertures 14 b, 16 b and focused (e.g., via one or moreion lens) into the mass analyzer 70. Though the ion source probe isgenerally described herein as an electrospray electrode 64, it should beappreciated that any number of different ionization techniques known inthe art for ionizing liquid samples and modified in accordance with thepresent teachings can be utilized as the ion source 60. By way ofnon-limiting example, the ion source 60 can be an electrosprayionization device, a nebulizer assisted electrospray device, a chemicalionization device, a nebulizer assisted atomization device, aphotoionization device, a laser ionization device, a thermosprayionization device, or a sonic spray ionization device.

As shown in FIG. 1, the exemplary ion source 60 can optionally include asource 63 of pressurized gas (e.g. nitrogen, air, or noble gas) thatsupplies a high velocity nebulizing gas flow which surrounds the outletend of the electrospray electrode 64 and interacts with the liquiddischarged therefrom to enhance the formation of the sample plume andthe ion release within the plume for sampling by 14 b and 16 b, e.g.,via the interaction of the high speed nebulizing flow and jet of liquidsample. The nebulizer gas can be supplied at a variety of flow rates,for example, in a range from about 0.1 L/min to about 20 L/min, whichcan also be controlled under the influence of controller 80 (e.g., viaopening and/or closing valve 65). In accordance with various aspects ofthe present teachings, it will be appreciated that the flow rate of thenebulizer gas can be adjusted (e.g., under the influence of controller80) such that the flow rate of liquid within the sampling probe 30 canbe adjusted based, for example, on suction/aspiration force generated bythe interaction of the nebulizer gas and the desorption solvent as it isbeing discharged from the electrospray electrode 64 (e.g., due to theVenturi effect).

In the depicted embodiment, the ionization chamber 12 can be maintainedat an atmospheric pressure, though in some embodiments, the ionizationchamber 12 can be evacuated to a pressure lower than atmosphericpressure. The ionization chamber 12, within which analytes desorbed fromthe substrate 20 can be ionized as the desorption solvent is dischargedfrom the electrospray electrode 64, is separated from a gas curtainchamber 14 by a plate 14 a having a curtain plate aperture 14 b. Asshown, a vacuum chamber 16, which houses the mass analyzer 70, isseparated from the curtain chamber 14 by a plate 16 a having a vacuumchamber sampling orifice 16 b. The curtain chamber 14 and vacuum chamber16 can be maintained at a selected pressure(s) (e.g., the same ordifferent sub-atmospheric pressures, a pressure lower than theionization chamber) by evacuation through one or more vacuum pump ports18.

It will also be appreciated by a person skilled in the art and in lightof the teachings herein that the mass analyzer 70 can have a variety ofconfigurations. Generally, the mass analyzer 70 is configured to process(e.g., filter, sort, dissociate, detect, etc.) sample ions generated bythe ion source 60. By way of non-limiting example, the mass analyzer 70can be a triple quadrupole mass spectrometer, or any other mass analyzerknown in the art and modified in accordance with the teachings herein.Other non-limiting, exemplary mass spectrometer systems that can bemodified in accordance various aspects of the systems, devices, andmethods disclosed herein can be found, for example, in an articleentitled “Product ion scanning using a Q-q-Q_(linear) ion trap (Q TRAP®)mass spectrometer,” authored by James W. Hager and J. C. Yves Le Blancand published in Rapid Communications in Mass Spectrometry (2003; 17:1056-1064), and U.S. Pat. No. 7,923,681, entitled “Collision Cell forMass Spectrometer,” which are hereby incorporated by reference in theirentireties. Other configurations, including but not limited to thosedescribed herein and others known to those skilled in the art, can alsobe utilized in conjunction with the systems, devices, and methodsdisclosed herein. For instance other suitable mass spectrometers mayinclude single quadrupole, triple quadrupole, ToF, trap, and hybridanalyzers. It will further be appreciated that any number of additionalelements can be included in the system 10 including, for example, an ionmobility spectrometer (e.g., a differential mobility spectrometer) thatis disposed between the ionization chamber 12 and the mass analyzer 70and is configured to separate ions based on their mobility through adrift gas in high- and low-fields rather than their mass-to-chargeratio). Additionally, it will be appreciated that the mass analyzer 70may comprise a detector that can detect the ions which pass through theanalyzer 70 and, for example, may supply a signal indicative of thenumber of ions per second that are detected.

The sampling probe 30 can have a variety of configurations but generallyincludes an open end by which the liquid delivered from the reservoir 50is open to the atmosphere, thus exhibiting a liquid-air interface. Theopen end can further be configured to receive therethrough a samplecontaining or suspected of containing one or more analytes. By way ofnon-limiting example, in some embodiments the sample may comprise aliquid sample that can be introduced (e.g., injected, pipetted,acoustically injected) directly into the liquid present within thesample space. It will likewise be appreciated by those skilled in theart in light of the teachings herein that any liquid (e.g., solvent)suitable for directly receiving a liquid sample, for example, andamenable to the ionization process can be provided by the reservoir 50in accordance with various aspects of the present teachings. In otherembodiments, the sample may comprise a solid sample that may beintroduced directly into the liquid present within the sample space fordissolution.

Alternatively, as shown in FIG. 1, the sample can be introduced via asample substrate 20 that can be inserted into the liquid within thesample space of the sampling probe 30. In various aspects, the samplesubstrate 20 can comprise a substrate having functionalized surfaces(e.g., a solid-phase microextraction (SPME) substrate, surface-coatedmagnetic particles) to which the analytes of interest have beenadsorbed. In such aspects, the liquid provided by reservoir 50 cancomprise a desorption solvent such that at least a portion of theabsorbed analytes are desorbed from the coated surface into thedesorption solvent upon insertion of the coated portion of the substrate20. It will be appreciated by those skilled in the art that in suchaspects any desorption solvent effective to desorb analytes from asubstrate 20 (e.g., a SPME device) and amenable to the ionizationprocess is suitable for use in the present teachings. U.S. Pat. No.5,691,205, entitled “Method and Devise for Solid Phase Microextractionand Desorption,” and PCT Pub. No. WO2015188282 entitled “A Probe forExtraction of Molecules of Interest from a Sample,” the teachings ofwhich are hereby incorporated by reference in their entireties, describeexemplary sampling substrates suitable for use in accordance withvarious aspects of the present teachings.

With reference now to FIG. 2, an exemplary sampling probe 30 forreceiving a liquid sample or sample substrate 20 through the open end ofthe probe and suitable for use in the system of FIG. 1 is schematicallydepicted. As shown, the exemplary sampling probe 30 is generallydisposed between the reservoir 50 and ion source 60 and provides a fluidpathway therebetween such that analytes entrained within the liquidprovided by the reservoir 50 (e.g., desorption solvent) can be deliveredto and ionized by the ion source 60. The sampling probe 30 can have avariety of configurations for receiving a liquid sample through its openend or sampling desorbed analytes from a substrate, but in the depictedexemplary configuration includes an outer tube (e.g., outer capillarytube 32) extending from a proximal end 32 a to a distal end 32 b and aninner tube (e.g., inner capillary tube 34) disposed co-axially withinthe outer capillary tube 32. As shown, the inner capillary tube 34 alsoextends from a proximal end 34 a to a distal end 34 b. The innercapillary tube 34 comprises an axial bore providing a fluid channeltherethrough, which as shown in the exemplary embodiment of FIG. 2defines a sampling conduit 36 through which liquid can be transmittedfrom the substrate sampling probe 30 to the ion source 60 via the probeoutlet conduit 44 c (i.e., the sampling conduit 36 can be fluidlycoupled to the inner bore of the electrospray electrode 64 via the fluidhandling system 40). On the other hand, the annular space between theinner surface of the outer capillary tube 32 and the outer surface ofthe inner capillary tube 34 can define a solvent conduit 38 extendingfrom an inlet end coupled to the solvent source 50 (e.g., via the probeinlet conduit 44 b) to an outlet end (adjacent the distal end 34 b ofthe inner capillary tube 34). In some exemplary aspects of the presentteachings, the distal end 34 b of the inner capillary tube 34 can berecessed relative to the distal end 32 b of the outer capillary tube 32(e.g., by a distance h as shown in FIG. 2) so as to define a distalfluid chamber 35 of the substrate sampling probe 30 that extends betweenand is defined by the distal end 34 b of the inner capillary 34 and thedistal end 32 b of the outer capillary tube 32. Thus, the distal fluidchamber 35 represents the space adapted to contain fluid between theopen distal end of the substrate sampling probe 30 and the distal end 34b of the inner capillary tube 34. Further, as indicated by the arrows ofFIG. 2 within the sampling probe 30, the solvent conduit 38 is in fluidcommunication with the sampling conduit 36 via this distal fluid chamber35. In this manner, fluid that is delivered to the distal fluid chamber35 through the solvent conduit 38 can enter the inlet end of thesampling conduit 36 for subsequent transmission to the ion source 60. Itshould be appreciated that though the inner capillary tube 34 isdescribed above and shown in FIG. 2 as defining the sampling conduit 36and the annular space between the inner capillary tube 34 and the outercapillary tube 32 defines the solvent conduit 38, the conduit defined bythe inner capillary tube 34 can instead be coupled to the solvent source50 (so as to define the solvent conduit) and the annular space betweenthe inner and outer capillaries 34, 32 can be coupled to the ion source60 (so as to define the sampling conduit).

It will be appreciated that sampling probes in accordance with thepresent teachings can also have a variety of configuration and sizes,with the sampling probe 30 of FIG. 2 representing an exemplarydepiction. By way of non-limiting example, the dimensions of an innerdiameter of the inner capillary tube 34 can be in a range from about 1micron to about 1 mm (e.g., 200 microns), with exemplary dimensions ofthe outer diameter of the inner capillary tube 34 being in a range fromabout 100 microns to about 3 or 4 millimeters (e.g., 360 microns). Alsoby way of example, the dimensions of the inner diameter of the outercapillary tube 32 can be in a range from about 100 microns to about 3 or4 millimeters (e.g., 450 microns), with the typical dimensions of theouter diameter of the outer capillary tube 32 being in a range fromabout 150 microns to about 3 or 4 millimeters (e.g., 950 microns). Thecross-sectional shapes of the inner capillary tube 34 and/or the outercapillary tube 32 can be circular, elliptical, super-elliptical (i.e.,shaped like a super-ellipse), or even polygonal (e.g., square). Further,though the exemplary sampling probe 30 is depicted in FIG. 2 as beingopen at its upper end, it will be appreciated that sampling probessuitable for use in the system of FIG. 1 and modified in accordance withthe present teachings can be oriented in a variety of orientations(e.g., upside down) as described, for example, in U.S. Pub. No.20130294971 entitled “Surface Sampling Concentration and Reaction Probe”and U.S. Pub. No. 20140216177 entitled “Method and System for Formationand Withdrawal of a Sample From a Surface to be Analyzed,” the teachingof which are hereby incorporated by reference in their entireties. Othernon-limiting, exemplary sampling probes that can be modified inaccordance various aspects of the systems, devices, and methodsdisclosed herein can be found, for example, in an article entitled “Anopen port sampling interface for liquid introduction atmosphericpressure ionization mass spectrometry,” authored by Van Berkel et al.and published in Rapid Communication in Mass Spectrometry 29(19),1749-1756, which is incorporated by reference in its entirety.

As shown in FIG. 2, an exemplary SPME substrate 20 having a coatedsurface 22 to which analytes can be adsorbed, as described, for example,PCT Pub. No. WO2015188282 entitled “A Probe for Extraction of Moleculesof Interest from a Sample,” the teachings of which are herebyincorporated by reference in its entirety, is schematically depicted asbeing inserted through the open end of the substrate sampling probe 30such that the coated surface 22 is at least partially disposed in thedesorption solvent (e.g., the desorption solvent within the distal fluidchamber 35). As shown in FIG. 2, by way of non-limiting example, theexemplary substrate 20 can comprise an extended surface 22 upon which aSPME extraction phase (e.g., layer) has been coated and to which one ormore analytes of interest can be adsorbed during extraction from asample. Upon the coated surface 22 being inserted into the distal fluidchamber 35, the desorption solvent within the distal fluid chamber 35can be effective to desorb at least a portion of the one or moreanalytes adsorbed on the coated surface 22 such that the desorbedanalytes can flow with the desorption solvent into the inlet of thesampling conduit 36. Substrates for use in systems and methods inaccordance with the present teachings are generally able to be at leastpartially inserted into a fluid pathway provided by a substrate samplingprobe 30 such that the desorption solvent provided thereby is effectiveto desorb one or more analytes of interest from the substrate, thoughthe substrate configuration (e.g., particles, fibers, blades,micro-tips, pins, or mesh) and/or coating (e.g., HLB-PAN, C18-PAN,antibodies, etc.) is not particularly limited. Indeed, any knownsubstrate and coating chemistries known in the art or hereafterdeveloped and modified in accordance with the present teachings can beused in the methods and systems disclosed herein. Other exemplary SPMEdevices suitable for use in accordance with various aspects of thepresent teachings are described, for example, in U.S. Pat. No.5,691,205, entitled “Method and Devise for Solid Phase Microextractionand Desorption,” the teachings of which are hereby incorporated byreference in their entireties.

As shown in FIG. 2, the reservoir 50 (e.g., source of desorption solventor other liquid) can be fluidly coupled to the solvent conduit 38 via asupply conduit 44 b through which liquid can be delivered at a selectedvolumetric rate (e.g., under the influence of pump 43 of FIG. 1). Anydesorption solvent effective to desorb analytes from a substrate 20(e.g., a SPME device) and amenable to the ionization process is suitablefor use in the present teachings. Additionally or alternatively, it willbe appreciated that one or more pumping mechanisms can likewise beprovided for controlling the volumetric flow rate through the samplingconduit 36 and/or the electrospray electrode 64 of the ion source 60,the volumetric flow rates selected to be the same or different from thatprovided by the pump 43. By way of example and as noted above, changesto the flow rate of the nebulizer gas can be effective to adjust thevolumetric flow rate through the sampling conduit 36.

As noted above, the sampling probe 30 of FIG. 2 additionally includes anultrasonic transmitter 95 coupled to an outer surface of the outerconduit for generating ultrasound energy that can propagate at leastthrough the sampling probe 30 and liquid within the sample space 35.Though the transmitter 95 is depicted as being coupled adjacent thedistal end 32 b of the outer capillary 32, it will be appreciated thatthe transmitter can be directly or indirectly coupled to any portion ofthe sampling probe 30 (e.g., via clamping, adhesion, magneticattraction) or integrated within the sampling probe at a variety oflocations effective to generate vibrations within the sample substrate20, the sampling probe 30, and/or the liquid within the sampling probe35 in accordance with various aspects of the present teachings asotherwise discussed herein. In some aspects, for example, thetransmitter 95 can be disposed in the fluid flow path through thesampling probe 35. By way of non-limiting example, an ultrasonictransmitter 95 coupled to the sampling probe as shown for example inFIG. 2 can be configured to generate ultrasonic waves on a substantiallyconstant basis (e.g., under the control of controller 80) so thatultrasonic waves are continually propagated within the sampling probe 30and the liquid accessible by its open end. However, in other aspects,the controller 80, operatively coupled to the ultrasonic transmitter 95,can generate control signals such that the ultrasound energy isgenerated at selected intervals automatically (e.g., according to aprotocol) or manually by the user, for example, only upon insertion of asample substrate 20 within the desorption solvent of the sample space35. In various aspects, the controller 80 can be integrated within theultrasonic transmitter 95 or may be a separate device connected to theultrasonic transmitter 95. For example, though in some implementationsthe ultrasound energy may not be effective to increase elutionefficiency from a sold-phase substrate upon which analytes are adsorbedas otherwise discussed herein (e.g., during the introduction of a liquidsample to the solvent within the sample space 35), it will nonethelessbe appreciated in accordance with various aspects of the presentteachings that the provision of ultrasound energy to the liquid withinthe sampling probe can also be effective to remove bubbles prior to theliquid transmitted to the ion source 60 via the sampling conduit 36. Insuch aspects, for example, that the degassing of liquid beingtransmitted to the ion source 60 can be performed substantiallycontinuously so as to prevent any bubbles present in the solvent flow,whether during sampling or between samplings, from being discharged bythe ion source 60.

With reference now to FIG. 3, another exemplary sample substrate 20 andsampling probe 30 configured to receive the sample substrate 20 (or aliquid sample) through the probe's open end is schematically depicted.As shown, the exemplary sampling probe 30 is substantially identical tothat depicted in FIG. 2, but differs in that the depicted sampling probe30 does not include an ultrasound transmitter coupled thereto. To thecontrary, in the exemplary implementation of the system of FIG. 1 asshown in FIG. 3, the ultrasonic transmitter 95 is coupled to the samplesubstrate 20 itself so as to generate vibrations in at least the coatedsurface portion 22 of the substrate 20 to which the analytes areadsorbed. As otherwise discussed herein, activation of the ultrasonictransmitter 95 upon insertion of the substrate 20 within the samplingspace 35 can be effective to increase the desorption efficiency ofanalytes therefrom. It will be appreciated in light of the presentteachings that the transmitter 95 need not be coupled directly to thesample substrate, but instead may be coupled to a substrate holder forgripping the sample substrate 20, for example. In various exemplaryaspects, the exemplary system 10 can include an actuation mechanism (notshown) such as a robotic arm, stage electromechanical translator, and/orstep motor that can be coupled to a sample holder so as to grip, hold,or otherwise couple to a sampling substrate 20 for automatedintroduction into the sample space 35. In such aspects, the ultrasonictransmitter can be coupled to the actuation mechanism or sample arm in aposition so as to cause the propagation of ultrasonic energy to thesample substrate 20. One exemplary robotic system suitable for use inaccordance with the present teachings is the Concept-96 autosamplermarketed by PAS Technologies). In accordance with an exemplary automatedworkflow, the actuation mechanism can under the control of thecontroller 80 introduce the substrate 20 into the sample space 35 of thesampling probe 30, with the controller activating the ultrasonictransmitter 95 associated therewith at a time corresponding to theinsertion of the substrate 20. It will further be appreciated that thesame or different actuation mechanism can likewise be utilized in acomplete sample preparation workflow including, for example,conditioning the substrate (e.g., coating or otherwise functionalizingthe surface to enable extraction of an analyte of interest),extraction/enrichment of the analytes from the sample (e.g., byimmersing the coated surface in the sample, with or without vortexing),rinsing the extracted sample (e.g., by immersing the substrate 20 havinganalytes adsorbed thereto in H₂O so as to remove some interferingmolecules, salts, proteins, etc.), and inserting the rinsed substrate 20within the sample space of the sampling probe 30.

With reference now to FIGS. 4A-C and FIG. 5, exemplary MS data areprovided depicting the improvement in the detected signals when applyingultrasound energy to the system 10 in accordance with various aspects ofthe present teachings. The experimental conditions utilized to generateFIGS. 4A-C were identical except for the inclusion of an ultrasonictransmitter as follows: no ultrasound energy was applied during sampling(FIG. 4A), an ultrasound transducer coupled to the sampling probe 30 wasutilized to generated ultrasound energy (FIG. 4C); an ultrasoundtransducer coupled to the sampling substrate 20 was utilized togenerated ultrasound energy (as in FIG. 4C). In particular, theultrasound energy applied to generate FIGS. 4B and 4C had a frequency ofabout 25 kHz. The samples comprised SPME fibers (marketed by Supelco)that were extracted in a sample of with clenbuterol. As shown in FIGS.4A-4C, experimental conditions in which ultrasound energy was appliedduring sampling (i.e., FIGS. 4B and 4C) resulted in approximately a 50%in signal intensity relative to the conditions in which no ultrasoundenergy was applied (i.e., FIG. 4A).

With specific reference now to FIG. 5, similar results were obtainedutilizing SPME blades (a metal substrate having both sides comprising acoated membrane as described in and PCT Pub. No. WO2015188282). As shownin FIG. 5, even greater signal enhancement (maximum signal intensity)was observed under the ultrasound-applied conditions relative to theconditions without ultrasound applied as compared to the relativeincrease depicted in FIGS. 4A-C. Without being bound by any particulartheory, this substantial increase may be due to improved propagation ofthe ultrasound energy through the metal SPME blade relative to the SPMEfiber.

In addition to utilizing ultrasound energy to improve desorption and/ordegas the liquid being delivered to the ion source (e.g., removingbubbles) as otherwise discussed herein, in some additional oralternative aspects of the present teachings, the ultrasound transmitter95 can be utilized as part of a feedback control system for controllingthe surface profile of the liquid-air interface within the samplingprobe's port. In some aspects, for example, the system of FIG. 1 caninclude both an ultrasonic transmitter for generating ultrasound energyand an ultrasound detector (e.g., which can be separate or integratedwith an ultrasonic transducer) that can be disposed relative to thetransmitter so as to detect the ultrasound energy that is reflected fromthe liquid-air interface. Ultrasound detectors 90 suitable for use inaccordance with the present teachings can have a variety ofconfigurations but are generally configured to convert ultrasound wavesinto an electrical signal, for example, that is indicative of the liquidlevel in the sampling probe 30 (e.g., based on return time of thereflected ultrasound waves). As discussed below, in such aspects, thecontroller 80 can be configured to generate control signals configuredto automatically adjust (e.g., without human intervention) the flow rateof the liquid into and/or out of a sampling probe to be selectivelyadjusted so as to maintain a desired liquid-air interface within thesampling port and a stable and reproducible analyte flow of consistentdilution to the ion source, thereby increasing the reproducibilityand/or accuracy of the MS analysis. Additionally or alternatively, thefeedback control can utilize the detected ultrasound energy so as toprovide for the automated adjustment of the surface profile of theliquid-air interface in accordance with a change in the desired setpoint according to an experimental workflow (e.g., automated adjustmentbetween an interface corresponding to a vortex sampling set point and anoverflow cleaning set point between samplings).

With reference to FIGS. 1 and 6, the system 10 includes an ultrasounddetector 90 for generating data indicative of the surface profile (e.g.,shape) of the liquid-air interface and a controller 80 operativelycoupled thereto so as to receive the data and adjust the flow rates ofliquid within the sampling probe 30. In accordance with various aspectsof the present teachings, the control signals generated by thecontroller 80 can automatically maintain and/or adjust the surfaceprofile to be a desired profile (e.g., without human intervention) bycontrolling the speed of the pump 43 and/or the flow rate of nebulizergas provided by the nebulizer gas source 63 to the outlet end of theelectrospray electrode 64, by way of non-limiting example. It will beappreciated that such a controller 80 can be implemented in a variety ofmanners in accordance with the present teachings, but generallycomprises one or more processors configured to analyze the dataindicative of the surface profile of the liquid-air interface and/orgenerate control signals for controlling the operations of variouselements of the system 10 as otherwise discussed herein. By way ofnon-limiting example, the controller 80 can be in the form of a digitalcontroller configured to process (e.g., via an algorithm) the dataprovided by the ultrasound detector 90 and provide real-time adjustmentsto the surface profile.

With reference specifically to FIG. 6, another exemplary sampling probe30 configured to receive the sample substrate 20 (or a liquid sample)through the probe's open end is schematically depicted in accordancewith various aspects of the present teachings. As shown, the exemplarysampling probe 30 is substantially identical to that depicted in FIG. 2,but differs in that the ultrasonic transmitter 95 is coupled to thesampling probe so as to direct its ultrasound energy at the liquid-airinterface. In particular, the ultrasonic transmitter 95 is disposedbelow the sampling conduit 36 so as to direct the ultrasound energysubstantially at the center of the liquid-air interface and which can bereflected thereat for detection by the ultrasound detector 90. That is,the transmitter can propagate ultrasound waves from below the conduitwall 44 c into the liquid, which upon traveling to the interface, arereflected at the phase boundary. The reflected ultrasound signal canreturn to and be detected by the ultrasound detector 90, with the returntime data being used by the controller 80 to determine the surfaceprofile (e.g., liquid level) of the liquid-air interface. As discussedin detail below with reference to FIG. 7, the liquid-air interface cantake on a variety of surface configurations or profiles at the open end,and the ultrasound energy will exhibit a reduced return time ifreflected from the center of the liquid-air interface depicted in FIG.7A (super-critical vortex surface profile) relative to that depicted inFIG. 7E (convex surface profile). In this manner, the controller 80 canadditionally or alternatively control the flow rate of the desorptionsolvent within the sampling probe 30 in accordance with various aspectsof the present teachings by adjusting one or more of a pump and/or valve65 for controlling the pressure or flow rate of the nebulizer gas. Byway of non-limiting example, the controller 80 can be configured tomaintain the flow rate of liquid provided by the pump 43 assubstantially constant, while accounting for changes in experimentalconditions (e.g., temperature effects, instability of the pump 43,changes of solvent/sample composition, for example, resulting in changesin sample/solvent viscosity, introduction rate/volume of liquid samplesinto the sample space 35) by adjusting the flow of nebulizer gasprovided from the nebulizer source 63 to thereby adjust the flow ofliquid within the sampling probe 30 in accordance with the presentteachings. Alternatively or additionally, it will be appreciated thatthe flow rate of the pump 43 can be adjusted under the influence of thecontroller so as to adjust and/or maintain the surface profile of theliquid-air interface. For example, in implementations in which anebulizer gas is not provided or the nebulizer gas pressure must remainfixed due to conditions of the ion source 60 or within the ionizationchamber 12, the controller 80 can modify the surface profile of theliquid-air interface by increasing or decreasing the speed of the pump43.

Depending on the liquid flow rates within the solvent conduit 38 and thesampling conduit 36, the liquid within the sample space 35 may take on avariety of surface configurations or profiles at the open end. Feedbackcontrol systems in accordance with various aspects of the presentteachings are configured to detect and/or monitor the surface profile(e.g., shape) of the liquid-air interface at the sample space 35 and toadjust the volumetric flow rates through the various channels of thesampling probe 30 and/or the electrospray electrode 44 so as to controlthe surface profile. Depending on the relationship of the volumetricflow rate into the sampling probe 30 (e.g., via solvent conduit 38,which can be primarily due to action of the pump 43) and the volumetricflow rate of the liquid from the sample space 35 to the ion source 60(e.g., via the sampling conduit 36, which can be primarily due to theeffect of the nebulizer gas), various liquid conditions can be formed inthe sampling port. With reference now to FIG. 7A-F, various exemplarysurface profiles of the liquid-air interface are depicted, with eachrepresenting a potential surface profile that can be detected bydetector 90 in accordance with the present teachings: super-criticalvortex (FIG. 7A); critical vortex (FIG. 7B); subcritical vortex (FIG.7C); balanced (FIG. 7D); convex (FIG. 7E); and convex spill over (FIG.7F). As shown schematically in FIG. 7A, when the liquid-air interfaceexhibits the super-critical vortex profile, the minimum height of theliquid-air interface is below the level of the distal end 34 b of theinner capillary 34, while the maximum height of the interface is at thelevel of the distal end 32 b of the outer capillary 32. As shown in FIG.7B, in liquid-air interfaces exhibiting a critical vortex shape, theminimum height of the liquid-air interface is at about the level of theof the distal end 34 b of the inner capillary 34, while the maximumheight of the interface is at the level of the distal end 32 b of theouter capillary 32. In the subcritical profile of FIG. 7C, the minimumheight of the liquid-air interface is between the level of the distalend 34 b of the inner capillary 34 and the distal end 32 b of the outercapillary 32, with the maximum height of the interface being at thelevel of the distal end 32 b of the outer capillary 32. In the balancedprofile of FIG. 7D, the liquid-air interface is substantially planar atthe level of the distal end 32 b of the outer capillary 32, while in theconvex profile (FIG. 7E) the maximum height of the liquid-air interfaceis above the level of the distal end 32 b of the outer capillary 32 soas to form a dome-like shape from the minimum height of the liquid-airinterface at the level of the distal end 32 b of the outer capillary.Finally, FIG. 7F depicts the convex spill over surface profile in whichthe maximum height of the liquid-air interface is above the level of thedistal end 32 b of the outer capillary 32 and the liquid overflows fromthe distal end 32 b thereof.

While the specific surface profile generated at the liquid-air interfacecan be a function of size of the various conduits, liquid temperature,surface tension, and other experimental conditions as noted otherwiseherein, the level of the liquid along the central longitudinal axiswithin the sample space (e.g., relative to the distal end 34 b of theinner capillary 34) can generally be increased by increasing thevolumetric flow rate of liquid into the sampling probe (e.g., viasolvent conduit 38), by decreasing the volumetric flow rate of liquidout of the sampling probe (e.g., via sampling conduit 36), or somecombination of the two. By way of example, the balanced condition (e.g.,a substantially planar liquid-air interface) can be achieved when thevolumetric flow rates are approximately equal. However, when the solventdelivery rate provided by the pump 43 is relatively low compared withthe solvent removal rate due to the aspiration force generated by thenebulizer gas, for example, a vortex surface profile can be formed as inFIGS. 7A-7C.

With reference now to FIGS. 8A-B, exemplary MS data are provideddepicting the variability in the detected signals under various flowconditions and liquid-air interface surface profile of a sampling probein accordance with various aspects of the present teachings. Theexperimental conditions utilized to generate FIGS. 8A-B were identicalexcept for the solvent flow rate provided by the solvent pump (e.g.,pump 43 of FIG. 1). In particular, the samples comprised injections of 2μL reserpine (in 50/50 MeOH:H₂0) into methanol being provided by thepump at 70 μL/min (FIG. 8A, low-flow conditions) and 150 μL/min (FIG.8B, overflow conditions), and the nebulizer gas was maintained at 90psi. Under the low-flow conditions, there may be less dilution effectdue to a decreased volume of liquid within which the analytes areintroduced, thereby resulting in the presence of higher, narrower peaksin the MS signal, as shown in the exemplary data of FIG. 8A. It will benoted that because some gas can be aspirated together with the liquid(e.g., as in the supercritical vortex condition of FIG. 7A), aberrationsor spikes in the MS data may also be observed when the bubbles aredischarged into the ionization chamber. On the other hand, when thesolvent delivery rate is relatively high as in experimental conditionsutilized to generate FIG. 8B, a dome-like, convex surface profile shapecan be formed (as in FIG. 7F). Though a more significant dilution effectmay be observed in high-flow/overflow conditions through the presence ofthe wider and less-intense MS peaks of FIG. 8B relative to those of FIG.8A, the convex profile may nonetheless be desired under certainexperimental conditions, for example, to enable an increased area of aSPME substrate having analytes adsorbed thereto to be disposed withindesorption solvent of the sample space. In any event, in comparing theMS signal of a plurality of substrates being inserted into the low andhigh flow rates of FIGS. 8A and 8B, respectively, it will be appreciatedby the person skilled in the art that the methods and systems describedherein for providing feedback control so as to maintain a stable,consistent surface profile (e.g., at the time of sample introduction forserial samplings) may be critical in ensuring the sensitivity, accuracy,and reproducibility of the resultant MS data.

With reference now to FIG. 9, a schematic block diagram of animplementation of a feedback control system in accordance with variousaspects of the present teachings is depicted. Though settings for theflow rates of the liquid provided by the pump 43 and/or the flow rateand/or pressure of nebulizer gas may initially be set at a valuecorresponding to an expected surface profile condition (e.g., bycontrolling the speed of the pump 43 and/or by adjusting the opening ofthe valve 65), variations in experimental conditions (e.g., temperature,surface tension of the liquid, instability in pump speed) may lead toundesired changes to the surface profile of the liquid-air interface.Thus, with the pump 43 providing liquid from the reservoir to the samplespace 35 of the sampling probe 30 and the nebulizer source 63 and valve65 controlling the aspiration force of the liquid from the samplingconduit 32, the ultrasound detector 90 (e.g., of FIG. 6) can generatedata indicative of a surface profile of the liquid-air interface withinthe open end of the sampling probe 30 (e.g., shape, liquid level at thecenter of the liquid-air interface). Based on the data received from thedetector 90, the controller 80 can then utilize a surface profilealgorithm to determine the present surface profile of the liquid-airinterface, and if necessary, generate control signals to adjust the pumpspeed or nebulizer gas pressure to modify the flow rate of liquid withinthe sampling probe 30 to produce a surface profile in accordance withthe surface set point (which can be selected by the user or determinedautomatically).

Use of the feedback control system of FIGS. 1 and 6 in accordance withvarious aspects of the present teachings will now be described withrespect to an exemplary automated workflow for analyzing a plurality ofsamples. The system 10 may be initiated by turning on the pump 43, ionsource 60, and gas flow provided by the nebulizer source 63. Afterallowing the system 10 to stabilize, the detector 90 can detect thesurface profile of the liquid-air interface of the sampling probe. Inaccordance with various aspects, the controller 80 can then compare thesurface profile data with a first reference surface profile (e.g., asampling set point, which can be pre-programmed or selected by the user)to determine if adjustments to the surface profile are necessary to bein accordance with the sampling set point prior to introducing a firstsample to the sample space 35. For example, if the surface profile doesnot correspond to the sampling set point, the controller 80 can increaseor decrease the speed of the pump 43 and/or the flow rate of nebulizergas accordingly as otherwise discussed herein. By way of non-limitingexample, the controller 80 can be configured to maintain the flow rateof liquid provided by the pump 43 substantially constant, whileaccounting for changes in experimental conditions (e.g., temperatureeffects, instability of the pump 43) by adjusting the flow of nebulizergas provided from the nebulizer source 63 such that the surface profileof the liquid-air interface is made to correspond to the sampling setpoint. Upon confirming and/or adjusting the surface profile to be inaccordance with the sampling set point, a first sample can then beintroduced within the liquid contained within the sample space 35.

In various aspects, the exemplary system 10 of FIG. 9 can include anactuation mechanism (not shown) such as a robotic arm, stageelectromechanical translator, and/or step motor that can be coupled to asample holder so as to grip, hold, or otherwise couple to a samplingsubstrate 20 for automated introduction into the sample space 35.Alternatively, the actuation mechanism can be configured to introduce(e.g., pipette, acoustically inject) a liquid sample within the samplespace 35, including, for example, aspirating the liquid sample from asample source (e.g., a 96 well plate), transporting the liquid sample tothe open end of the sampling probe 30, transporting a carrier platecontaining one or more samples to align with the open end, anddispensing the liquid sample into the solvent via the liquid-airinterface (e.g., including pipette injection as well as othernon-contact techniques including dispensers, such as by acousticdispensers or pneumatic dispensers, from an aligned sample well). Oneexemplary robotic system suitable for use in accordance with the presentteachings is the Concept-96 autosampler marketed by PAS Technologies).In accordance with an automated workflow, the actuation mechanism canunder the control of the controller 80 introduce the substrate 20 (or aliquid sample, for example) into the sample space 35 of the samplingprobe 30 after the controller 80 determines that the surface profilecorresponds to the desired sampling surface profile based on theultrasound energy generated by the ultrasonic transmitter 95 that isreflected from the liquid-air interface and detected by the ultrasounddetector 90. It will further be appreciated that the same or differentactuation mechanism can likewise be utilized in a complete samplepreparation workflow including, for example, conditioning the substrate(e.g., coating or otherwise functionalizing the surface to enableextraction of an analyte of interest), extraction/enrichment of theanalytes from the sample (e.g., by immersing the coated surface in thesample, with or without vortexing), rinsing the extracted sample (e.g.,by immersing the substrate 20 having analytes adsorbed thereto in H₂O soas to remove some interfering molecules, salts, proteins, etc.), andinserting the rinsed substrate 20 within the sample space of thesampling probe 30.

As discussed otherwise herein, analytes introduced into the sample space(e.g., desorbed from a sample substrate 20 by the desorption solventprovided from the reservoir 50) and entrained within the liquid (e.g.,desorption solvent) can then be delivered to the ion source 60 and massanalyzer 70 for ionization and mass spectrometric analysis. After theanalytes from the first sample have been transmitted from the samplespace 35 (e.g., after removal of a sampling substrate 20), in someaspects, the controller 80 can be configured to effect an increase thevolumetric flow rate of liquid from the reservoir 50 to the sample space35 so as to temporarily overflow liquid through the open end of thesampling probe 30 before another substrate 20 is inserted therein,thereby cleaning residual sample deposited by the withdrawn substrateand/or preventing any airborne material from being transmitted into thesampling conduit 36 in between serial samplings. By way of example,after the first substrate 20 has been removed, the controller 80 cancompare the data generated by the ultrasound detector 90 to a secondreference surface profile (e.g., a cleaning set point having a surfaceprofile as in FIG. 7E) and automatically adjust the flow rates providedby one of the pump 43 and nebulizer source 63 to correspond to thesurface profile of the cleaning set point for a given duration. Prior tointroduction of a second sample, the controller 80 can then utilize thedata generated by the surface profile detector 90 to re-adjust thesurface profile to match the sampling profile utilized during samplingfrom the first substrate. In this manner, the feedback control systemcan account for variations in experimental condition between samplings,while helping to ensure consistent dilution effects, thereby increasingthe accuracy and reproducibility of the MS data between multiplesamplings. In addition, in accordance various aspects of the presentteachings, the same ultrasound energy that is generated by theultrasonic transmitter 95 for detection as part of the feedback controlsystem can likewise provide for increased desorption efficiency (e.g.,from a solid-phase sample substrate) and/or improved degassing asotherwise discussed herein.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting. While the applicant's teachingsare described in conjunction with various embodiments, it is notintended that the applicant's teachings be limited to such embodiments.On the contrary, the applicant's teachings encompass variousalternatives, modifications, and equivalents, as will be appreciated bythose of skill in the art.

What is claimed is:
 1. A system for analyzing a chemical composition ofa specimen, comprising: a reservoir for storing a liquid; a samplingprobe having an open end partially defining a sample space configured toreceive liquid from the reservoir, said liquid within the sample spacefurther configured to receive through the open end one or more analytesof a sample; a pump for delivering the liquid from the reservoir to anion source via the sample space, wherein the ion source is configured todischarge the liquid having said one or more analytes entrained thereininto an ionization chamber in fluid communication with a samplingorifice of a mass spectrometer; an ultrasonic transmitter for applyingultrasound energy to at least one of the liquid within the sample space,the sampling probe, and a sample substrate to be inserted into theliquid within the sample space.
 2. The system of claim 1, wherein thesample comprises a liquid sample containing said one or more analytes.3. The system of claim 1, wherein the liquid comprises a desorptionsolvent and the sample comprises a sample substrate having one or moreanalytes adsorbed thereto such that at least a portion of said one ormore analytes are desorbed therefrom into the desorption solvent withinthe sample space.
 4. The system of claim 3, wherein the ultrasonictransmitter is coupled to the sample substrate and is configured toapply ultrasound energy to the sample substrate upon insertion thereofinto the sample space, wherein the ultrasound energy facilitatesdesorption into the liquid of one or more analytes adsorbed onto asurface of the sample substrate.
 5. The system of claim 3, wherein theultrasound energy is configured to increase a temperature of the liquidwithin the sample space.
 6. The system of claim 3, further comprising acontroller configured to generate control signals for activating theultrasonic transmitter upon insertion of the sample substrate withininto the sample space.
 7. The system of claim 1, wherein the ultrasonictransmitter is coupled to the sampling probe so as to apply ultrasoundenergy to the sampling probe and the liquid therewithin.
 8. The systemof claim 1, wherein the ultrasound energy is configured to increaseagitation of the liquid within the sample space.
 9. The system of claim1, wherein the ultrasonic transmitter is configured to degas the liquidprovided by the pump prior to the liquid being delivered to the ionsource.
 10. The system of claim 1, further comprising: an ultrasounddetector configured to detect ultrasound energy reflected from aliquid-air interface in the sample space so as to generate dataindicative of a surface profile of the liquid-air interface at the openend of the sampling probe; and a controller operatively coupled to theultrasound detector and configured to generate control signals based onthe surface profile data for adjusting the surface profile of theliquid-air interface, wherein the control signals generated by thecontroller are configured to adjust the flow rate of liquid within thesampling probe by adjusting at least one of the flow rate of liquidprovided by the pump and the flow rate of a nebulizer gas that surroundsthe discharge end of the ion source.
 11. The system of claim 1, whereinthe sampling probe comprises: an outer capillary tube extending from aproximal end to a distal end; and an inner capillary tube extending froma proximal end to a distal end and disposed within said outer capillarytube, wherein said distal end of the inner capillary tube is recessedrelative to the distal end of the outer capillary tube so as to definethe sample space between the distal end of the inner capillary tube, aportion of an inner wall of the outer capillary tube, and the distal endof the outer capillary tube, wherein said inner and outer capillarytubes define a solvent conduit and a sampling conduit in fluidcommunication with one another via said sample space, said solventconduit extending from an inlet end configured to receive solvent fromthe reservoir to an outlet end terminating at said sample space, andsaid sampling conduit extending from an inlet end commencing at saidsample space for receiving from the sample space desorption solvent inwhich the desorbed analytes are entrained to an outlet end fluidlycoupled to the ion source.
 12. A method for chemical analysis,comprising: providing a flow of liquid to a sampling probe, saidsampling probe having an open end partially defining a sample spaceconfigured to receive the liquid and further configured to receivethrough the open end one or more analytes of a sample into the liquidwithin the sample space; directing a flow of the liquid having the oneor more analytes entrained therein from the sample space to an ionsource configured to discharge the liquid having the one or moreanalytes entrained therein into an ionization chamber in fluidcommunication with a sampling orifice of a mass spectrometer; applyingultrasound energy to at least one of the liquid within the sample space,the sampling probe, and a sample substrate during insertion thereof intothe liquid within the sample space; and discharging the liquid havingthe one or more analytes entrained therein into the ionization chamberfor ionization therein.
 13. The method of claim 12, wherein theultrasound energy is generated by an ultrasonic transmitter coupled toat least one of the sampling probe and the sample substrate, the methodfurther comprising activating the ultrasonic transmitter upon insertionof a sampling probe into the sample space so as to facilitate desorptionof one or more analytes adsorbed thereto.
 14. The method of claim 13,wherein the ultrasonic transmitter is coupled to the sample substrateand is configured to apply ultrasound waves to the sample substrate uponinsertion thereof into the sample space, wherein the ultrasound wavesfacilitate desorption into the liquid within the sample space of one ormore analytes adsorbed onto a surface of the sample substrate.
 15. Themethod of claim 13, wherein the ultrasound energy is configured tofacilitate desorption into the liquid of one or more analytes adsorbedonto a surface of the sample substrate via at least one of increasingagitation of the liquid in the sample space and increasing thetemperature of the liquid in the sample space.
 16. The method of claim12, wherein the ultrasound energy is configured to degas the liquidprovided by the pump prior to the liquid being delivered to the ionsource.
 17. The method of claim 12, wherein applying ultrasound energycomprises directing the ultrasound energy through the liquid toward aliquid-air interface at the open end of the sampling probe, the methodfurther comprising: detecting the reflected ultrasound energy togenerate data indicative of a surface profile of the liquid-airinterface at the open end of the sampling probe; and based on thesurface profile data, adjusting the flow rate of the liquid within thesampling probe so as to adjust the surface profile of the liquid-airinterface.
 18. A system for analyzing a chemical composition of aspecimen, comprising: a reservoir for storing a liquid; a sampling probehaving an open end partially defining a sample space configured toreceive liquid from the reservoir, said liquid within the sample spacefurther configured to receive through the open end one or more analytesof a sample; a pump for delivering the liquid from the reservoir to anion source via the sample space, wherein the ion source is configured todischarge the liquid having said one or more analytes entrained thereininto an ionization chamber in fluid communication with a samplingorifice of a mass spectrometer; an ultrasonic transmitter for applyingultrasound energy to at least one of the liquid within the sample space,the sampling probe, and a sample substrate to be inserted into theliquid within the sample space an ultrasound detector for detecting theultrasound energy reflected from the liquid-air interface at the openend of the sampling probe so as to generate data indicative of a surfaceprofile of the liquid-air interface; and a controller configured togenerate control signals based on the surface profile data for adjustingthe surface profile of the liquid-air interface.
 19. The system of claim1, wherein the ultrasonic transmitter and the detector are integratedwithin an ultrasonic transducer.
 20. The system of claim 1, wherein theultrasonic transmitter and the ultrasound detector are disposed so as toreflect and detect respectively the level of liquid within the samplingspace at the center thereof.